RELATIONS OF AIR AND WATER TO TEMPERATURE AND LIFE. 275 



trade, or otlier moisturo-beariiig winds. This territory extends from 

 Arabia uortlieastward beyond tlie Lake of Balkasli into Siberia, a vast 

 extent of conntry, larger than Europe — a dry, rainless desert, hot in 

 summer and cold in winter. Part of tills region is from 6,000 to 7,000 

 feet above the level of the sea, part below the sea level, yet neither 

 height uor depression makes any difterence in this arid land. For- 

 merly sections of these countries were thickly populated. The Aral 

 and Caspian basins were called the " Garden of the world." In Meso- 

 ])otamia were Ninevah, Bagdad, and Babylon; in Persia, Susa and 

 Persopolis. Historians tell us of great cities, flourishing empires, 

 where now is only a barien and sandy desert. We do not know whether 

 the climate has changed or whether in ancient days the country was 

 thoroughly irrigated, and now through neglect has been buried deep 

 in the sand of the desert. Although tbur-hfths of Asia are either 

 desert or mountainous land and are only scantily inhabited, two-thirds 

 of the population of the world are found within its borders. 



